13th International Conference on Fracture June 16–21, 2013, Beijing, China -2- 2. Experimental results of single lap joint In this study, the experimental results obtained by Park et al [10] will be used in order to examine the validation of evaluation method of the adhesive strength. In the experiments, Aluminum alloy 6061-T6 and epoxy resin were used as adherent and adhesive, respectively. Table 1 shows the mechanical properties of the adherent and adhesive. Figure 1 shows the specimen configuration. Table 2 and Figure 2 show the experimental tensile adhesive strength Pa f . As for all specimens except for specimen A10, the relation between the load and displacement is almost linear. Therefore, it can be considered that the fractures were caused by the unstable growth of the interfacial debonding crack which was initiated from the corner edge. The results bring the validation of the evaluation based on the intensity of the singular stress field. When the overlap length becomes long under constant adhesive thickness condition, the adhesive strength tends to increase; when the adhesive layer becomes thick under constant overlap length, the adhesive strength does not change remarkablely. Figure 3 shows the average shear stress at the fracture, τc. When l2 is smaller than about 15mm, the τc becomes constant at about 28.3MPa. However, when l2 is larger than about 15mm, the τc tends to decrease. The fracture is caused by the general yielding of the adhesive layer when the overlap length is small enough; in this case, the τc becomes constant. In this study, it is supposed that the cohesive fracture occurs when l2 < 15mm and the adhesive fracture occurs when l2 > 15mm. Therefore, although the fracture criterion for SLJ having small overlap length can be described by the average shear stress at the fracture, that for SLJ having long overlap length cannot be described by the stress. Table 1 Material properties 10) Material E [GPa] ν Adherent 6061-T6 68.9 0.30 Adhesive Epoxy resin 4.2 0.45 E : Young’s modulus, ν : Poisson ratio Figure 1 Specimen configurations 10) Table 2 Experimental tensile adhesive strength by Park et al 10) (a) constant 2 = t condition (b) constant 2 = l condition Specimen 2l [mm] 2t [mm] Pa f [kN] Specimen 2l [mm] 2t [mm] Pa f [kN] A10 10 0.15 6.87 A25 25 0.15 14.17 A15 15 0.15 10.57 A25-30 25 0.30 14.32 A20 20 0.15 12.41 A25-45 25 0.45 14.26 A25 25 0.15 14.17 A25-90 25 0.90 14.19 A30 30 0.15 14.56 A30 30 0.15 14.56 A35 35 0.15 16.41 A30-30 30 0.30 16.91 A40 40 0.15 18.09 A30-45 30 0.45 16.12 A50 50 0.15 18.22 A30-90 30 0.90 15.37
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